1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate and a semiconductor substrate manufacturing apparatus.
2. Description of the Related Art
In recent years, instead of a bulk silicon wafer, integrated circuits using an SOI (silicon on insulator) substrate have been developed. By utilizing characteristics of a thin single crystal silicon layer formed over an insulating layer, transistors formed in the integrated circuit can be electrically separated from each other completely. Further, each transistor can be formed as a fully-depleted transistor, and thus a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
As a method for manufacturing an SOI substrate, a hydrogen-ion-implantation separation method in which hydrogen ion implantation and separation are combined is known. A typical process of a hydrogen-ion-implantation separation method is described below.
First, hydrogen ions are implanted into a silicon wafer to form an ion implantation layer at a predetermined depth from the surface. Next, a silicon oxide film is formed by oxidizing another silicon wafer which serves as a base substrate. After that, the silicon wafer into which hydrogen ions are implanted is attached firmly to the silicon oxide film of the another silicon wafer, so that the two silicon wafers are bonded to each other. Then, heat treatment is performed so that the wafer is cleaved with the ion implantation layer used as a cleaved surface.
There is a known method in which a single crystal silicon layer is formed over a glass substrate by a hydrogen-ion-implantation separation method (e.g., Reference 1: Japanese Published Patent Application No. H11-097379). In Reference 1, a separation plane is mechanically polished in order to remove a defect layer formed by ion implantation or difference in level which is several to several tens of nanometers in height in the separation plane.